This invention relates generally to flowing mercury cathode electrolytic cells and, more specifically, to an improved flow baffle that is insertable into the brine inlet trough.
Flowing mercury cathode electrolytic cells have been employed for a substantial number of years to produce chlorine and caustic throughout the world. Electrolytic cells are generally used to decompose solutions of alkali metal compounds. In the flowing mercury type of electrolytic cell, a mercury cathode is provided which flows along the bottom of the cell. A plurality of anodes are usually composed of plate-like elements supported from above with their surfaces parallel to the surface of the flowing mercury and spaced a short distance above the flowing mercury.
This distance between the anodes and the cathode in a flowing mercury cathode type of electrolytic cell is important since the inter-electrode distance should be as small as possible to reduce the consumption of energy required to accomplish the electrolysis. However, if the distance is too small between the anodes and the cathodes, secondary reactions may occur which reduce the efficiency of the cell.
Short circuits are a substantial problem in flowing mercury cathode type of electrolytic cells and are a source of this undesirable reduction in cell efficiency. Any direct contact between the anodes and the flowing mercury cathodes will form a short circuit. This short circuiting can burn-out the anodes where such cathode-anode contact occurs.
In a flowing mercury cathode type of electrolytic cell an aqueous solution of an alkali metal halide, such as for example, sodium chloride, flows through the cell and immerses the anodes and part of the anode supporting structure. A thin layer of the solution occupies the space between the upper surface of the flowing mercury cathode and the bottom surface of the anode. DC current passes through the anodes, through this thin layer of the aqueous solution of the alkali metal compound and to the mercury cathode, which is at the bottom of the cell. This flow of current provides the energy to generate the product chlorine gas.
This aqueous solution of the alkali metal halide is normally called brine. The brine is sent into the electrolytic cell through an inlet trough adjacent one end of the cell box. This trough is near the flowing mercury cathode on the bottom of the cell and the initial suspended anodes. If the flow rate and path of brine into the cell is not controlled, the brine can create turbulence in the flowing mercury cathode which can cause the mercury to splatter onto the anode surfaces immediately above the cathode. This, then, results in the short circuiting problem.
Prior efforts, such as that described in U.S. Pat. No. 4,152,237 of McAllister et al and assigned to the assignee of the present invention, have attempted to solve this problem by controlling the flow rate of brine into the cell box. This has proven unsuccessful, however, since splashing of the flowing mercury cathode still occurs because of the velocity of the infed brine. When this splashing occurs and contact is made with the anodes which are suspended overhead, the anodes are prematurely eaten away because of the short circuiting. This is especially a problem for the first or inlet set of anodes nearest the inlet ,; brine trough.
Also, a "ripple effect" in the mercury is caused by the turbulent manner in which the inlet brine flows into the cell. This rippling along the top surface of the flowing mercury varies the distance between the individual anodes and the flowing mercury cathode along the length of the cell, thereby varying the optimum inter-electrode distance. This less than optimum inter-electrode distance thereby increases power costs during the operation of the cell. One solution to this "ripple effect" problem has been to increase the inter-electrode gap. However, this then further increases the power cost of the operation of the cell, especially when the automatic adjusters used in some commercial mercury cells raise all of the anodes, normally 10 or 12 sets or channels, and not just the initial set adjacent the inlet brine trough.
The foregoing problems are solved in the design of the apparatus comprising the present invention.